This invention relates to improvements in the selection of materials for multilayered liners in shaped charges to enhance the formation of high energy impact for oil well perforators and other shaped charge applications, such as military applications.
Following the experience of World War II in which portable anti-tank weapons were developed using explosive charges in various shapes to enhance the armor penetration capacity of such projectiles, it became apparent that such shaped projectiles could be employed in other areas. Specifically, in the field of oil well perforating devices, the so-called shaped charge quickly came into use for the purpose of enhancing rate of flow in an oil well. The charge had a cavity or recess in the forward end of an explosive projectile, and the cavity was lined typically with a dense material such as copper. In use, when the explosive charge was ignited, the detonation wave engaged the metal liner, causing the liner to collapse inwardly upon itself into the cavity. As the collapsing liner reached the center of the cavity, a small forward portion of the liner formed an extremely high-velocity jet of energy which was then responsible for the relatively deep penetration achieved in early oil well perforating devices.
The remainder of the collapsed liner formed a large slug of material which followed the advancing energy jet at a much lower velocity and contributed little or nothing to penetration. The depth of penetration into the target by the jet depended then as it does today on the characteristics of the material of which the liner is made. In general, it is agreed that the liner material for a shaped charge should have a high density and be capable of flowing smoothly into a long jet. Subsequent years of experimentation in this field have brought several developments in an attempt to provide deeper penetration with greater efficiency. Nevertheless, the full potential of the shaped charge device was not achieved.
One of the problems perceived by experimenters in the field was that of the presence of the relatively massive slug which formed following the high velocity jet. In many instances, the slug tended to plug the hole formed by the jet thus inhibiting or preventing the flow of oil. Attempts were undertaken to provide for the inclusion in shaped charge liners of materials which would cause the slug to vaporize or liquify. Other attempts were made to remove the presence of the plug by using liners made of two different materials, i.e., an outer easily vaporizable metal liner next to the explosive charge, and an inner higher density metal liner surrounding the cavity. Changes were proposed in the shapes of the cavity, including conical, hemispherical and others. These efforts were mostly directed toward minimizing the establishment or the effect of the slug. Many other efforts concentrated in the area of altering the physical state of the liner material, such as granularizing or sintering the liner material also to minimize the effect of the slug.
While some of these developments have provided small or moderate increases in the momentum of the jet, there has been no recognition of the fundamental scientific principles and the necessary qualities in liner materials which should be considered in combining the amounts of explosive charge with the optimum liner materials and designs to transfer the greatest amount of energy from the explosive detonation to the high-velocity jet.
It is therefore an objective of this invention to provide criteria for the selection of materials used in multi-layered liners in combination with explosive materials in shaped charges.
It is also an objective of this invention to provide means for increasing the transmission of explosive energy from the detonating explosive to the high velocity jet of a shaped charge.
It is a further objective to provide for two or more layers of material in shaped charges to minimize shattering of the inner layer next to the cavity.
It is still a further objective to provide for reduced reflection of explosive energy from the interface within multi-layered liners and from the interface between the liner and the explosive.
These and further objectives will become obvious in view of the following explanation of the invention.